The term “acyl lactylate” refers to a compound having an acyl group from a fatty acid attached to one (monolactylates) or several lactic acid molecules (dilactylates and higher lactylates) and a proton (H+) or another cation attached to the terminal carboxylate. A representative acyl lactylate may possess the general structure:RCO—(O—CHCH3—CO)n—OHwherein RCO is the acyl radical of a fatty acid, R typically having from 3 to 35 carbon atoms, and n is an integer of from 1 to 10. The hydrocarbon chain (R) can be linear or branched, may be saturated or unsaturated and may be substituted by one or more hydroxyl groups.
Such lactylates are common food additives: several types of lactylate can function as emulsifiers or humectants in food items such as baked goods, cereals, chewing gums and desserts. An example of such use is disclosed in Boutte et al. Stearoyl-2-lactylates and oleoyl lactylates, Pages 206-225, Emulsifiers in Food Technology, R. J. Whitehurst ed., Blackwell Publishing Ltd., Oxford, UK (2004).
Other lactylates find use as surfactants, viscosity modifiers, emulsifiers, foam boosters and stabilizers in personal care applications: acyl lactylates may serve to improve skin feel, skin softness and moisturization and reduce tackiness during a wet to dry transition after product application.
Osipow, et al., Fatty Acid Lactylates, pp. 1-12 (1969) describes the use of stearoyl lactylic acid and its sodium salt as a cosmetic gelling agent. Interestingly this citation also teaches that caproyl lactylate and sodium lauroyl lactylate are non-toxic and can exhibit anti-microbial activity. Developing this concept, EP 2 082 739 A1 (Purac Biochem BV) describes the use of lactylates for preventing or treating infections caused by gram-positive bacteria in animals.
To enjoy utility in regulated applications such as cosmetics and functional nutritional products, it will be evident that the acyl lactylates need to be of high purity. The present application is directed to the purification of synthesized acyl lactylates.
U.S. Pat. No. 2,733,252 (Thompson et al.) describes a process for the preparation of acyl lactylates in which lactic acid and a fatty acid are subjected to direct esterification at a temperature of from 100° C. to 250° C. in the presence of an alkali catalyst. U.S. Pat. No. 2,789,992 (Thompson et al.) describes a process for synthesizing acyl lactylates by reacting lactic acid with an acid chloride of fatty acid. WO2014/167069 (Purac Biochem BV) describes a process for the preparation of a salt of a fatty acid ester of inter alia lactic acid which comprises heating an oil, comprising a triglyceride fatty acid ester in admixture with a catalyst and a salt of lactic acid at a temperature at or above the melting temperature of the lactic acid and subjecting the mixture to ester interchange.
The reaction products obtained by the aforementioned processes usually contain a considerable amount of both lactic acid and fatty acid, derived from the starting materials, in addition to the desired fatty acid ester of lactic acid. Thus the end product of the reaction may be regarded as a mixture of the desired product acyl lactylate, higher order lactylates, lactic acid and free fatty acid or their salts. These species may be present in the mixture as salts, typically alkali metal, ammonium or amine salts.
The provision of such a mixture is obviously at odds with the commercial requirement for acyl lactylate products of higher purity. It is therefore an object of the present invention to provide a commercially feasible process whereby the components of these mixtures may be separated.
Problematically both fatty acid and acyl lactylate, possess the same long fatty acid chain which is strongly hydrophobic. It would therefore be expected that these products, and more particularly products having larger acyl groups, could not be separated by making use of a liquid-liquid extraction procedure: classical liquid-liquid extractions make use of the principle that the solubility of two compounds differ in two different phases which cannot be mixed together.
Furthermore, the mixture of fatty acid and acyl lactylates is known to have strong emulsifying properties. A skilled person would consider that these properties would render it difficult to separate the phases in the liquid-liquid extraction procedure.